Many persons have endeavored to design alternative systems of public and private transportation. Examples of systems illustrative of the prior work done in this field would include the system engineered by the Aerospace Corporation in Los Angeles, California, the Cabintaxi PRT, the Monocab, and the H-Bahn systems. Although each of the above-described systems has evidenced development of the theory of personal rapid transit, each has exhibited shortcomings in simplicity of operation, lightness of overall weight, economy of manufacture, and reliability and safety of operation.
The determination of a vehicle's direction while moving along a stationary track can be solved in many ways. The conventional passenger and freight railroad in use at the present time employs parallel track rails which are themselves moved into position to allow a railway train to be guided onto the proper track. These moving track systems are plagued by numerous problems which find their root in the fact that the track rails themselves must be movable. Consequently, snow, ice, and debris hinder the movement of the tracks and decrease the overall efficiency of the system.
It is known that a monorail system can be designed which allows passage of vehicles through diverging and converging portions of the track without moving parts or switches on the track, rail or guideway itself. Many systems are known which accomplish this result, but all of the known systems are hampered by problems. For example, in a system employing hanging vehicles beneath an overhead rail, the following disadvantages are present regardless of the switching mechanism employed: (1) The guideway must be substantially higher than with a system including vehicles supported above a track, and support posts must be cantilevered to allow room for the car to pass by the post. (2) If the bogie that supports the vehicle is contained within the guideway, a means must be provided to allow the support wheels to pass over the slot through which the vehicle is hung in the switch section. This typically requires that the support wheels be relieved of their supporting weight during switching operations. This problem appears to be inherent in this design and is difficult to overcome economically and simply.
Two examples of the switching mechanisms known in hanging systems are interesting. German Offenlegungschrift No. 24 29 887 laid open for public inspection Jan. 9, 1975, shows a switch mechanism having switch wheels on the ends of a rocker arm. The rocker arm includes joints to allow the switch wheels to remain parallel to each other as they selectively engage a flange. The force of engagement of the switch wheels and the flange will not pass through the pivot point on which the rocker arm pivots. This arrangement requires a substantial lock mechanism to prevent the torque on the pivot point created by the engagement of the wheel on the flange from rotating the rocker arm during use. Similarly, U.S. Pat. No. 4,290,367 issued Sept. 22, 1982, illustrates a device which includes a switch mechanism having torque exerted on the rocker arm due to the geometry of the arrangement. Again, the force of interaction of the rollers on the rails will not pass through the pivot point.
Vehicles which are side mounted on a guideway have the advantage that they may be turned around by passing the vehicle around the end of the guideway and in the reverse direction on the opposite side. This is satisfactory for vehicles operating along a single line but switching the cars between lines is difficult and consequently the side mounted design is less than satisfactory for laying out a complete network. Also, supporting the vehicle on the side of a guideway requires that the wheel supports resist both the weight of the vehicle as well as the bending moment of the vehicle. Thus, the total wheel load is greater than in a top or bottom-mounted configuration, thereby increasing the total road resistance experienced by the wheels.
In a top-mounted vehicle, one in which the passenger or cargo compartment rides above a guideway or the like, the lateral stability of the vehicle is a consideration. Assuring the stability of the vehicle, particularly when switching, while experiencing crosswind conditions or uneven passenger loading, complicates the design and operation of the system. The ideal top-mounted system would include a guideway of minimum size and weight allowing a system of minimum complexity and expense. A reduction in overall size of the guideway allows the system to operate more economically than would a system with a large elevated roadway. However, a guideway narrower than the vehicle it supports increases the lateral stability concerns and intensifies the need for an improved switching mechanism wherein no moving parts are contained within the guideway and the vehicle remains stable during switching.
Ideally, the switch mechanism is contained completely within the bogie of a vehicle. The switch mechanism should positively insure that the vehicle will negotiate any point of convergence or divergence in the guideway safely. The switch mechanism should maintain its position while in the switching section of the guideway without the need for auxiliary devices. Additionally, the switch mechanism should be designed so that at no time can the wheel of the switch mechanism strike the guide channel of the guideway thus presenting the possibility of damage to the switching mechanism or the guideway. The switch mechanism should also be stable, in that it will remain in a given position during operation of the vehicle along the guideway between switching sections or areas of convergence or divergence. The switch mechanism should be designed so that it is positively secured during use and will not stop at an intermediate position due to a power or motor failure. Further, the time required to throw the switch should be minimized to allow rapid and sure selection of the vehicle path, and to minimize the required distance between switching sections. Additionally, the vehicle should be equipped with a signaling device which positively indicates the position of the switching mechanism. It should also be possible to throw the switch from wayside even if the vehicle is disconnected from its power supply.
Advances in the field of mass transit, in the areas of safety, reliability and dependable operation are important as no system can attract ridership if the system has a poor record of past performance. The switching devices presently available have shortcomings in these areas, and therefore there is a need for an improved switching device.